1. Field of the Invention
This invention concerns, improvements in and relating to alpha and/or beta particle detection in small spaces, particularly but not exclusively through the detection of Ions produced by the passage of alpha and/or beta particles through a medium such as air.
2. Present State of the Art
Direct detection of alpha particles emitted into air is only possible if the detector is presented very close to the source. Alpha particles decay over a range of 4 to 5 cm and as a consequence are not directly detectable beyond that range.
Techniques have been developed in which the ions generated by the passage of the alpha particles over this range are detected at a remote location so as to give an indication of the level of contamination present. These techniques rely upon as much of the ions generated as possible being detected as the number of ions, and hence signal currents involved, are very small.
In many applications, the effective path of the alpha particles from the source is shortened by a collision between the alpha particle and an opposing surface. Such occasions occur in narrow diameter pipes, for instance, as well as in confined locations on the surfaces of pieces of apparatus, such as heat exchange surfaces on motors and the like, as well as elsewhere. The effective path of the alpha particles in such situations is so short that very few ions are actually generated before the alpha particle loses its energy through collision with further surfaces. Existing techniques for detecting these ions face problems in such circumstances due to the small number of ions generated.
Due to their high energies the length of the path over which beta particles decay in media such as air is far longer. As a consequence even in relatively large sized pipes and the like relatively few ions are generated through unit of path length and the effective path is shortened by a collision between the beta particle and opposing surface. As a consequence of the low number of ions generated beta particle monitoring using ions detection has not been pursued.